The present invention is directed to methods and apparatus for detecting and quantifying allergens in foodstuffs, and, more particularly, concerns peanut allergens, antigens, monoclonal antibodies having specificity for peanut allergens, hybridoma cell lines which produce the monoclonal antibodies and immunoassay methods and apparatus including the monoclonal antibodies for detecting and quantifying peanut allergens in food-processing equipment and materials as well as natural, processed, and finished foods.
The ingestion of peanuts is a common cause of food hypersensitivity reactions. Symptoms can vary from mild abdominal discomfort to severe anaphylaxis. In a recent report by Yunginger et al., "Fatal Food-Induced Anaphylaxis", Journal of the American Medical Association 1988; 260:1450-2, four of seven patients who experienced fatal anaphylaxis died after peanut ingestion. All four of these patients unknowingly had eaten peanut in food prepared and consumed away from home. In the most recent studies involving children and food challenges, peanut is among the three leading foods that cause food hypersensitivity reactions.
The increasing use of peanut products in our food supply has served to aggravate the problem of peanut allergy. Peanuts, generally in the form of peanut butter, are introduced into the American diet at a very young age. Some children react on challenge to peanut on their first known exposure, indicating that they had been sensitized in utero, by breast feeding, or by an unknown exposure. Unlike other food sensitivities in children, long-term follow-up studies of up to fourteen years indicate that peanut hypersensitivity is rarely outgrown.
It is important for peanut-sensitive individuals to have a means of recognizing and avoiding peanut-containing products. Unfortunately, peanut allergens have been identified in non-peanut foodstuffs manufactured on common processing equipment that were inadequately cleaned. Peanut products that serve as substitutes for other nuts in candles are not uncommon. In patients suffering from extrinsic asthma, hayfever, or atopic eczema, symptoms develop immediately after exposure to specific allergens. This immediate type of allergy is a function of a special type of serum antibodies called reagins. These reagins have been identified as belonging to the IgE class of immunoglobulins. Radioimmunoassays (RIA) have been developed to measure the level of circulating allergen specific IgE in human blood samples.
For example, Pharmacia Diagnostics AB, Uppsala, Sweden, manufactures a Phadebas RAST.RTM. radioimmunoassay (U.S. Pat. Nos. 3,645,852 and 3,720,760). The Phadebas Rast.RTM. radioimmunoassay is an in vitro test system based on the Radio Allegro Sorbent Test principle for determination of circulating specific IgE antibodies. The allergen of interest is covalently coupled to a solid phase. The allergen is reacted with a patient serum sample containing both allergen specific and non-specific IgE. The allergen reacts with the specific IgE in the patient sample. After washing away non-specific IgE, radioactively labeled antibodies against IgE are added forming a complex. Then unbound radioactively labeled anti-IgE is washed away. Next, the radioactivity of the bound complex is measured in a gamma counter. The more bound radioactivity found, the more specific IgE present in the sample. To classify the test results, patient counts are compared directly with counts of reference sera run in parallel. This system is designed for use in testing allergens including grass, tree, weed pollens, house dust, mites, foods, insects, epidermals, molds, drugs, occupational allergens, and parasites.
Pharmacia Diagnostics AB, Uppsala, Sweden also manufactures a Pharmacia IgE RIA Ultra solid-phase, sandwich radioimmunoassay for quantitative determination of total IgE in human serum. The serum concentration of IgE is significantly elevated in most patients with allergic diseases, such as extrinsic asthma, hayfever, and atopic disease. In this system, a monoclonal anti-IgE is covalently coupled to a test tube wall. This monoclonal reacts with the IgE in the samples during a first incubation. The tubes are then washed and radioactively labeled anti-IgE reacts with the bound IgE during a second incubation. After the second incubation, unbound radioactively labeled anti-IgE is washed away. The radioactivity in the tube is then measured and is directly proportional to the concentration of the IgE in the sample.
The use of a radioimmunoassay to detect peanut allergens in food processing materials and finished foods is described in a Keating et al. article entitled "Immunoassay of Peanut Allergens in Food Processing Materials and Finished Foods", appearing in the Journal of Allergy Clinical Immunology 1990; 86:41-4. To quantitate trace amounts of peanut allergens in food processing materials and finished foods, there was established a solid-phase radioimmunoassay inhibition using pooled sera from five peanut-sensitive subjects and roasted peanut meal extract covalently linked to polyacrylamide beads. Test samples were extracted, dialyzed, lyophilized, and reconstituted at 10 to 125 mg of dry weight per ml concentrations. The peanut allergen content of test samples was expressed relative to a reference extract of roasted peanut meal that was assigned an arbitrary potency of 100,000 U/ml. In confectionary products spiked with varying quantities of peanut, the recovery of peanut allergen ranged from 31% to 94%. The sensitivity of the assay was 2.5 U/mg of dry weight from the samples. Peanut allergens were undetectable in virgin vegetable oil used to roast peanuts, but 600 to 760 U/mg of dry weight were present in oil after varying periods of use. The allergen content of used oil was reduced to 8 U/mg of dry weight by filtration and steam cleaning. The availability of such a radioimmunoassay provides a way of monitoring finished food products for potential allergens.
In light of the foregoing, there is a need for an improved immunoassay for detecting and quantifying specific peanut allergens in food processing materials, equipment, and raw, processed, and finished foods.